ON PREVENTING THE DRY-ROT IN WOOD, Y5 



tiie external cold, that the chief or common mode In which 

 the wall is cooled is not by the access of the cold air into 

 the room, but by the passage of heat from the wall itself 

 into the ,cold air without. We may however so far avail our- but in part, 

 selves of this principle, ps to exclude ua much cold air as 

 we can, by shutting up the windows and chimnies of unin- 

 habited rooms during the severity of frost. 



It may farther be suggested, that as, during a thaw, the Shutting up ^ 

 air, being warmer than in frost, has a greater quantity of [^^^j^^^"^^ 

 water in form of vapour mixed with it, shutting up a room ficient. 

 on such occasions may, by retarding the admission of warmer 

 jair so charged with vapour, allo\y time for the walls to ac- 

 quire an equable temperature through their substance from, 

 without, so as to anticip^ite any condensation on their surface 

 which might occur from the free admission of the external 

 air. To this 1 only answer, as before, that rooms according 

 to the common construction cannot be excluded from com- 

 munication with the external air; and that, in fact, the 

 dampness does vmder these circumstances take place, though 

 the doors and windows are never opened. 



In all cases, however, there is one method of preventing The -wall 

 this species of dampness, which is infallible; and that is to Ju^cfendy^^* 

 keep every part of the internal surface of the wall in the warm by fire. 

 chamber or staircase sufficiently warm by good fires. With 

 this view all staircases Ought to have some means of receiv- 

 ing artificial warmth. 



If, notwithstanding this and the former precaution, a wall Dried if neceis- 

 should accidentally become damp, the next best expedient ^^^^' 

 is to dry it as quickly as possible by a free current of warrrj 

 air. 



This discussion, which at first sight might appear tedious 

 and irrelevant, will, 1 trust, no longer be thought so, when 

 it shall have been found necessary for the establishment of 

 9 principle on the subject more immediately before us. 



In order to show the analogy, let us take the simplest ex- Analogy inthe 

 •mple, which is that of a wainscotted room, unwarmed by case of dry-rot. 

 ^res. When tlie wainscot is colder than the air, it conden- 

 ses the vapour in "form of moisture. If that moisture were 

 fxposed to the influence of the sun and wind, the case 

 l^puld come under the former head of decay, which is that 



of 



